Replace Sass with PostCSS, include imports and nesting

assets/css/components/slides.css

@@ -0,0 +1,22 @@
+.slides {
+    background: url("../images/loading.gif") center no-repeat;
+    min-height: 275px;
+
+    @screen md {
+      & {
+        min-height: 375px;
+      }
+    }
+
+    @screen lg {
+      & {
+        min-height: 450px;
+      }
+    }
+
+    @screen xl {
+      & {
+        min-height: 560px;
+      }
+    }
+}